#!/usr/bin/env python

import sys, os, time, atexit
from signal import SIGTERM

class Daemon:
    """
    A generic daemon class.
   
    Usage: subclass the Daemon class and override the run() method
    """
    def __init__(self, pidfile='nbMon.pid', stdin='/dev/null', stdout='nbMon.log', stderr='nbMon.log'):
            self.stdin = stdin
            self.stdout = stdout
            self.stderr = stderr
            self.pidfile = pidfile
   
    def daemonize(self):
            """
            do the UNIX double-fork magic, see Stevens' "Advanced
            Programming in the UNIX Environment" for details (ISBN 0201563177)
            http://www.erlenstar.demon.co.uk/unix/faq_2.html#SEC16
            """
            try:
                    pid = os.fork()
                    if pid > 0:
                            # exit first parent
                            sys.exit(0)
            except OSError, e:
                    sys.stderr.write("fork #1 failed: %d (%s)\n" % (e.errno, e.strerror))
                    sys.exit(1)
   
            # decouple from parent environment
            #os.chdir("/")
            os.setsid()
            os.umask(0)
   
            # do second fork
            try:
                    pid = os.fork()
                    if pid > 0:
                            # exit from second parent
                            sys.exit(0)
            except OSError, e:
                    sys.stderr.write("fork #2 failed: %d (%s)\n" % (e.errno, e.strerror))
                    sys.exit(1)
   
            # redirect standard file descriptors
            sys.stdout.flush()
            sys.stderr.flush()
            si = file(self.stdin, 'r')
            so = file(self.stdout, 'a+')
            se = file(self.stderr, 'a+', 0)
            os.dup2(si.fileno(), sys.stdin.fileno())
            os.dup2(so.fileno(), sys.stdout.fileno())
            os.dup2(se.fileno(), sys.stderr.fileno())
   
            # write pidfile
            atexit.register(self.delpid)
            pid = str(os.getpid())
            file(self.pidfile,'w+').write("%s\n" % pid)
   
    def delpid(self):
            os.remove(self.pidfile)

    def start(self):
            """
            Start the daemon
            """
            # Check for a pidfile to see if the daemon already runs
            try:
                    pf = file(self.pidfile,'r')
                    pid = int(pf.read().strip())
                    pf.close()
            except IOError:
                    pid = None
   
            if pid:
                    message = "pidfile %s already exist. Daemon already running?\n"
                    sys.stderr.write(message % self.pidfile)
                    sys.exit(1)
           
            # Start the daemon
            self.daemonize()
            self.run()

    def stop(self):
            """
            Stop the daemon
            """
            # Get the pid from the pidfile
            try:
                    pf = file(self.pidfile,'r')
                    pid = int(pf.read().strip())
                    pf.close()
            except IOError:
                    pid = None
   
            if not pid:
                    message = "pidfile %s does not exist. Daemon not running?\n"
                    sys.stderr.write(message % self.pidfile)
                    return # not an error in a restart

            # Try killing the daemon process       
            try:
                    while 1:
                            os.kill(pid, SIGTERM)
                            time.sleep(0.1)
            except OSError, err:
                    err = str(err)
                    if err.find("No such process") > 0:
                            if os.path.exists(self.pidfile):
                                    os.remove(self.pidfile)
                    else:
                            print str(err)
                            sys.exit(1)

    def restart(self):
            """
            Restart the daemon
            """
            self.stop()
            self.start()

    def run(self):
            """
            You should override this method when you subclass Daemon. It will be called after the process has been
            daemonized by start() or restart().
            """
